Covers of drinking receptacles which enable drinking of water contained in the receptacles without removing the covers are disclosed, for example, in Japanese Unexamined Patent Publication Nos. Hei 7-251854 and Hei 7-95907, and U.S. Pat. Nos. 4,099,642, 4,276,992 and 4,303,173.
These covers share a common constitution in that they each have a slant cover plate, with a top surface and a bottom surface, for covering a heat insulating receptacle at the open top and a rim surrounding the cover plate and that the cover plates each have a spout at the lowest level portion adjacent to the rim.
However, the cover disclosed in Japanese Unexamined Patent Publication No. Hei 7-251854 which is provided with a spout as described above and an air inlet has no closing member at the spout and air inlet. Accordingly, the spout and the air inlet are normally open, so that there is an apprehension in the heat insulating effect of the cover and that the water contained in the receptacle can leak through such openings, if the drinking receptacle is turned over inadvertently.
Meanwhile, the cover disclosed in Japanese Unexamined Patent Publication No. Hei 7-95907 is provided on the top surface of the cover plate with a pivotal stopper for opening and closing the spout. However, since this cover has no packing and is not of watertight structure, the temperature of water escapes through the clearance between the spout and the stopper, limiting its heat insulating effect. Further, if the drinking receptacle happens to be turned over, the water contained in the receptacle spills out. Besides, the operation of opening and closing the stopper by pivoting it on the top of the cover plate is not easy.
The covers disclosed in the above three U.S. Patents are each provided with a valve assembly having at the free end a valve element for closing the spout and a pair of resilient arms extended in the direction opposite to the valve element, and a push rod which has a cam surface formed at the free end and operates the valve assembly. The valve assembly is applied to the bottom surface of the cover plate with the aid of the resilient arms which urge the valve element to achieve watertight closure of the spout. The push rod penetrates an insertion opening formed in the rim to be retractable along the bottom surface of the cover plate, and the valve assembly is moved by the cam surface to be open by pushing the rear end protruding outward through the rim.
In the cover disclosed in U.S. Pat. No. 4,099,642, while the valve assembly and the push rod are oriented diametrically, one must grip the upper part of the receptacle having the greatest diameter when the rear end of the push rod protruding outward through the rim of the cover is pushed, so that the receptacle is too inconvenient to be held stably. In addition, since the rear end of the push rod is of relatively small size, it is hard to push directly with the thumb and requires some power.
In the covers disclosed in U.S. Pat. Nos. 4,276,99 and 4,303,173, the push rod is oriented orthogonal to the valve assembly and is designed to be pressed with a short lever provided on the rim.
If such covers are fitted on receptacles with handles, the lever is located above a handle, and thus the lever can be operated easily. However if the cover is fitted on a receptacle with no handle, the lever is hard to operate, because the spout and the lever are positioned at an angular interval of 90.degree..
It is an objective of the present invention to provide a drinking receptacle cover which exhibits excellent heat insulating effect and is free from spilling of water even if the receptacle is turned over and which enables opening and closing of the spout with small power, no matter whether the cup to which the cover is applied has a handle or not, to release the internal pressure when the spout is opened and secure inflow of the outside air through the air inlet, enabling smooth drinking of the water contained in the receptacle.